Turbocharged engines are well known in the art. A turbocharger may include a turbine wheel that is inserted in the exhaust path of the engine. Mechanically connected to the turbine is a compressor wheel that is located in the inlet manifold of the engine. As is known in the art, the engine exhaust causes the turbine wheel to rotate thereby causing the compressor wheel to compress the air entering the engine intake manifold. By compressing the air, a greater quantity of air can be introduced in the engine cylinders, thereby permitting a greater quantity of fuel to be injected, and in this manner, increasing the power output of the engine over a normally operated engine.
In some instances, compressing the air may cause too great a pressure increase in the intake manifold or too much pressure in the engine cylinder. In those cases, if the turbocharger is allowed to operate unrestrained, the engine might be damaged. A wastegate is often installed to prevent the pressure from exceeding a level at which engine damage might occur.
A wastegate is typically connected to both the intake and exhaust manifolds. When the pressure in the intake manifold approaches a level that might damage the engine, the wastegate opens a port in the engine's exhaust plumbing, which causes the exhaust gas to bypass the turbocharger turbine wheel. This, in turn, reduces the speed of the turbine, thereby reducing the compressing force exerted by the turbocharger compressor. In this manner, the wastegate helps to insure that the turbocharger does not create a damaging intake manifold pressure.
However, if the wastegate valve malfunctions, the bypass path around the turbocharger turbine wheel closes preventing exhaust gas from bypassing the turbine wheel. Thus, if the wastegate malfunctions, the turbocharger compressor can continue to compress air beyond the pressure level that might cause damage to the engine.
Other wastegate control systems are known in the prior art. For example, U.S. Pat. No. 5,121,604 discloses a closed loop control for a wastegate that attempts to regulate the intake manifold pressure according to a predetermined map that is a function of engine speed and other parameters. The disclosure discusses safeguards to protect against electrical failures. For example, a switch is provided that becomes active when the servo loop fails. By activating the switch, the control delivers a fixed command valve that is only a function of engine speed. In this manner, the intake manifold pressure is held below a level that might cause engine damage. However, the U.S. Pat. No. 5,121,604 patent does not disclose any safeguard to protect the engine in the event the wastegate valve itself fails.
Another example of a known wastegate control is disclosed in U.S. Pat. No. 4,646,834. This patent discloses a control that biases the wastegate valve to a predetermined position in the event of an electrical failure. That predetermined position will result in reduced pressure levels over the levels that would otherwise be permitted if the system were operating correctly. As with the U.S. Pat. No. 5,121,604 patent discussed above, this disclosure does not discuss a control system that protects against wastegate failure.
Also, neither these devices nor any other known control systems measure each engine's specific permissible boost pressure levels which can then be compared against current boost pressures to determine whether a wastegate valve has failed. Furthermore, in the prior art, control systems do not derate engine power output in the event of a wastegate failure.
The present invention overcomes the disadvantages of previous wastegate valves and wastegate controls. These and other advantages of the present invention will be understood from reading the specification in connection with the drawings and claims.